Chevrolet Corvette 1963 Repair & Tune-Up Manual page 170

SPARK PLUG DIAGNOSIS
Normal ' -
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APPEARANCE: This plug is typical of one'oper- ,,
ating normally.' The insulator nose varies froraa >
light tan<to grayish cplor yvitri, slight, electrbde'' ?
wear. The presence of .slight deposife is normal,
on used plugs and will' have" ho
on engine performance.-The spark; pltig^heat
range is correct Jorth^engine'and trie ,engine)s , •'
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running normally. ,
CAUSE: Propdrly running engiria'"^"
RECOMMENDATIpN: Before, reinstalling '.this ,
plug, the electrodes, shpuld;be cleaned and filejd
square: Set the gap tp sp'e'cif ications. I;f the plug ,
has been in service^for,mor'e
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miles, trje entire set 'should pfoi^ably/be^rje- *_
placed with a fresh set of the'sarhe
Incorrect Heat Range :/
APPEARANCE: Thp'effects of h^gfi terhpefature;
on a spark.plug are indicated by«,clean white,'-
often blistered, tabulator; This pa'n
companied by excessiye wear pf tHe'JBlect^ode,
and the absence of deposits. ,'
CAUSE: Check fof the, correct*'spark"rjjug,heat',
range: A plug which is too,hot fpr/fhe,engine.
can result in overheating: A car pp'erated'mpstly
at high speeds can require a;colde( plug: Arsd^
check ignition timing, coolipg^syslem level, fuel-,
mixture and leaking intake manrjplcl.>; > "•' ';;,',
RECOMMENDATIO'Nilf'all jgnitioh ,and engine,
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adjustments are kriowp'to^e'correct^'arid no
,other; malfunctipp' exists; install ''sparfc plugs
one-heat range colder."',••* V
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Photos Courtesy'Fram Corporation,
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adverse 'effect
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tharii'10r'i2^000, "
h'eat range.
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also be ac-
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Oil Deposits ^ \ '
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, APPEARANCE: Trie firing end of;the/plug\is
.covered with a-wet,oijy*cbating., ^' '^' j.')"
vcXuSE:T he,problem is ppo^oii cbntrpl.'On high
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• mileage enginps, oil is, leaking past'the^ings or
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valve guides irrto, thejcombustion-'chamber. A
, common cause is.also^a plugged PCV'valve,,
, .and a ruptured, fuel pump diaphragrri, cap 'also
cause this condition. C3il fouled plugsvsuch as
,,
•these are,often found,in'new?pr,recent.ly
hauled; engines,, before normal oi| control is
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(.achieved, and can'be cleaned and reinst^lied.^
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,<R*ECqMMeNDATION:'A,hotter spark plug'may
temporarily relieve the problem*, but Jhe engine
improbably irf need of work.
Carbon Deposits
;'APPEXRANCE: Carboh^oulipg'ls easily.'ideriti-
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'fied by.trie.prdsence of dryj'soft/black, ^obty
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•'deposits.. - , , './sV",
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CAUSE:' Changing th<r heat' range'cart'often'
•lea'd to carbon fouling, fis-can prolonged,! slow; >
'Stoi3-an'd-start;drivirigi'lri:he heat rangejs/cpr^
~ rept,'-carbon fciuTirig carijbe''attributed;to a.rich
fuel'mixture, sticking^ cKbke, clogged' air.
^blearier, w/qrn" breaker p'omts, ,relarded'!|mihg 'or-,
« low,compress)onMf only, on,e dr twd**pluigs 'are
, carbon; fouled, check for'corroded Wfc'r^c'ked
wiVesdfithe,affected'plugs.,Als6
''m']the distributor cap .between'ihe towers',^of
; affepted cylinders'."
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;RECOMMpNiDATldNrAfternhe .prbblerrys por-
' rected/tfies&'plugs^can^be
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' stalled it not worn severely.
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over-
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'Iopllfpf',pracks'
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